The visible spectrum of electromagnetic radiation observed the interaction of photons with surface plasmons nanoparticles Ag, Au, platinum group metals. W ool can be dyed with gold nanoparticles. For bimetallic nanoparticles observed only one lane swallowing like a monometallic particles. Once it is shifted compared to monometallic.  Bimetallic nanoparticles may give no visible spectrum characteristic  peak. Hence, not  the interaction of photons with surface plasmons nanoparticles. Wool can not be dyed with this nanoparticles.

Best regards.

Mrs/Miss/Mr Ain,

This depends on the element and its oxidation state in the corresponding NPs.

Dear Prof. Bojidarka B. Ivanova,

This is the visible spectrum of bimetallic nanoparticles. They give only metal nanoparticles having a plasmon resonance property. What oxidized state do you mean?

Best regards.

Mr. Mirgorod,

Let us starti with the fact that AuxAgy NPs, in particiular, exhibit lmax at about 480-440 nm. But in the case of the Mr. Ain's NPs there are not characteristic bands.

On the other hand, these NPs are obtained as non-stoichiometric AgxAuy compositions (x, y are within a wide range).

The quantification of such as compositions, in general, is difficult due to the fact that there is experimentally observed a broad oxidation peak of Ag. Furthermore this difficult the quantitation of the particle size as well. Electrochemical studies, for example, have shown a charge over the Ag ca. 10-14 C.This essentially assumes a different from '0' oxidation state.

Despite the fact that Au0 and Ag0 are with formal oxidation state '0' there are many evidences assuming 'CT effects'. In addition, there is a large body of literature devoted to theoretical elucidation in this context.

You should bear in mind that such as localized charges absent in cases of neutral monometallic particles (Nevertheless they are occurred in monometallic monocationic clusters of type [Mn]+ in gas - phase). Or this phenomenon is typical for multimetallic compositions in a general neutral state. In addition to many more phenomena which can occur in M1M2M-Mn alloys, again, in a general context. So these are properties addressed to the alloys. Despite the fact that alloys could have NPs sizes, of course.

(NB! We are talking about NPs of alloyds, not NPs of Agx@Auy)

So the questions about the oxidation state and charge (re)distribution/transfer (?!) in alloys are far from well understood. Moreover in so simple as electronic configurations elements like Au and Ag. There are even more complex cases of ''alloys''.

Do you known the nature of M-M bonds (?!) in a composition like Ag0.25Au0.75 with a localized charge on Ag? Because of there is lack of literature data.

In this context, in general, employment of UV-VIS spectroscopy studying the chemistry of such as compositions is completely unsuitable, even this is high speculative task. By contrast, a complementary employment of electrochemistry and quantum chemistry both experimentally and theoretically, should provide significantly more meaningfull information. Because of the fact that there are obtained non-stoichiometric compositions difficults employment of powder XRD as well as, due to lack of references.

I would like to look at two plasmon peak in hybrid  like Ag0.25Au0.75 with a localized charge on Ag. 

Regards.

Mr. Mirgorod,

I, in particular, have no measurements, furthermore the system is also an example of alloy with stoichiometry 1:3. But there are data in the literature about non-stoichiometric Ag0.17Au0.84, for example, and many more non-stoichiometric compositions and variations. In spite of in this case also lies the question associated with electronic configurations, in addition to questions reflecting charge localization andthus the oxidation state of such as bimetallic alloys and their NPs.

Mr. Mirgorod,

According to the content of this discussion, let us go through an example of quantum chemical computations of a AgAu3 model of alloy. You could pay attention to these very representative results (Attachment).

Let us describe the alloy system as a cyclic as molecular structure (Page 1). The optimization of the geometry yields to C2v symmetry.

The character of the Ag-Au bond cannot be described as pure ionic, however, becase of the natural ionicity is i = 0.6738. The analysis of the Laplacian density shows rather ionic and van der Waals nature (Page 1).

In addition there are shown the corresponding electronic configurations and orbital energies, including accounting for the spin-states of the electrons (Page 2). You should bear in mind that the data in page 2 cannot be correlated quantitatively, because of they are obtained using two completely different as philosophy methods. Nevertheless, a detail analysis of the available data sets indicates same correlations in qualitative terms.

Page 3 presents a theoretical TDDFT data within the UV-VIS region. As you might see from my representation of the theoretical spectrum as a figure, the so-called 'plasmonic' band, in fact, represents a structural set of sub-maxima, which corresponds and reflects a concrete electronic and molecular structure of the ensemble of AgAu3 atoms.

This short example illustrates in a clear form the obvious problem with the interpretation of the UV/VIS spectra of bimetallic alloys/NPs.

If we return to my previous posting, the problem is due to the fact that depending on the molecular and electronic structure there should have different profile within UV/VIS region (Page 3, UV-VIS spectrum and HOMO/LUMO figure).

Therefore, it is not, not only obvious, but even speculative, how to explain a basic observation of a set of UV-VIS bands of bimetallic alloys and their NPs - furthermore talking even not about non-stoichiometric compisitions - without knowledge of the molecular structure, electronic structure, and charge redistribution (oxidation state) of the atoms in these alloys/NPs.

An essential part of this posting is to reflect as well as the common view about the so-called 'plasmonic band' in NPs of alloys, showing that this is not just a structureless broad band. By contrast, its structure reflects a concrete electronic structure within the framework of a concrete molecular structure of interacting atoms in these NPs. In order to make this explanation more tangible, I should add that alloys/NPs with different structures shall exhibit close profiles within UV-VIS region. This fact makes UV-VIS as method inapplicable for a reliable analysis, even a qualitative one, in general.

Furthermore, the fact that there is a deviation from 'pure' type interactions, makes unsuitable the employment of the term 'plasmonic' for bimetallic alloys (Most probably not to all bimetallic alloys?!). We are talking, here, just for electronic spectra of alloys in the classical terms of the electronic spectroscopy of inorganics. The foundations are in the well known crystal and ligand field theories.